In recent years advances in biotechnology have led to the development and therapeutic use of novel recombinant polypeptides, including erythropoietin and granulocyte colony stimulating factor, to the benefit of many human patients. Increasing numbers of other polypeptides have since been discovered which exhibit biological activity in vitro. However, the characterization of target cells of these factors and the biological effects of the factors in vivo are essential for the identification of potential therapeutic applications in humans.
KGF is a known mitogen which has been previously identified as specific for epithelial cells, particularly keratinocytes. Rubin et al., Proc. Natl. Acad. Sci. USA, 86:802-806 (1989); Finch et al., Science, 245:752-755 (1989); Marchese et al., J. Cell. Phys. 144:326-332 (1990). Expression of messenger RNA for KGF has been detected in several stromal fibroblast cell lines derived from epithelial tissues of embryonic, neonatal and adult human sources, and in RNA extracted from normal adult kidneys and gastrointestinal tracts. Such RNA has not been detected in glial cells, lung cells, brain cells, or in a variety of epithelial cell lines that include squamous cell carcinomas, mammary epithelial cells, immortalized bronchial epithelial cells, immortalized keratinocytes, or primary keratinocyte cultures. Finch et al., Science, above. However, KGF is mitogenically active for the continuous mouse cell line, BALB/MK cells. Weissman and Aaronson, Cell, 32:599 (1983); also, see PNAS and Science, above. This observation supports evidence indicating a paracrine action of KGF in the skin, with production of KGF in the dermis (but not in the epidermis) and action on keratinocytes.
In addition, using the expression of keratins and filagrin genes it has been demonstrated that KGF influences the differentiation and maturation of keratinocytes. See J. Cell Phys., above.
Much of the aforementioned work investigating the biological activity of KGF has been carried out with recombinant KGF, which has permitted more widespread study of this factor. Published PCT patent application WO 90/08771 describes the purification of KGF from the conditioned medium of a human embryonic fibroblast cell line, partial amino acid sequencing of the isolated polypeptide, cloning of the gene, and expression in bacterial cells (E. coli) to achieve recombinant, biologically active KGF.
While the role of KGF as a stimulatory agent for keratinocytes in vitro has been clearly identified, much remains to be known regarding KGF as a growth factor, including additional types of cells for which it may be targeted, and the effect of KGF on such cells in vivo. This information is vital for an understanding of the full potential of KGF as a therapeutic agent.